Autonomous vehicles are being increasingly used for a variety of underwater applications. Some applications include gathering undersea data pertaining to seafloor mapping, and gathering data for chemical analysis for possible oil field exploration, with an increasing trend towards deep water field developments. The data gathering can be important, particularly in the case of deep water development for oil fields, because there is a much greater potential for larger finds than can be expected in more littoral regions. But to gather data, these autonomous vehicles will often contain components that cannot withstand a large pressure differential, such as onboard electronics, for example. Accordingly, these deep water vehicles will often employ a pressure compensation system for either an electrical subsystem such as a battery, or the complete electrical system, such as in the case of the Navy Advanced Tethered Vehicle. Other deep diving autonomous vehicles have components that must kept dry, in addition to being pressure sensitive. One way to accomplish this is to develop deep diving vehicles where the entire sensor and electrical package is kept dry by enclosing the package within a pressure vessel, which is itself pressure compensated.
However, the use of pressure vessels in the traditional way to protect electronic equipment from the undersea environment has its own costs. As pressures increase due to the deeper depths desired for exploration, the size, weight, and cost of pressure vessels required to house the selected vessel components increases as well, and the increase is exponential. One example of this is the comparison between the REMUS 100 and REMUS 6000 autonomous vehicles manufactured by Hydroid®. Both vehicles utilize the same electronics and software. However, to accommodate an increase in depth range from one hundred meters to six thousand meters (100 m to 6000 m), the vessel weight increases from eighty pounds to approximately two thousand pounds (80 lbs to 1950 lbs) to accommodate the stronger pressure vessels needed. Alternately, a combination of exotic material and heavy walled pressure vessels are used. But in addition to being heavy, the exotic materials used to manufacture such pressure vessels add a great deal of cost, which restricts their utility.
Still other pressure compensation systems use an inert, non-compressible fluid such as mineral oil, contained in a compressible volume pressure compensation system to protect batteries and electronics from the undersea environment. The advantage of using a liquid is that, there is little volume change as pressure increases. This allows for more compact system designs. Incompressible fluid filled systems are however heavy, require that additional buoyancy be added to the system to offset the mass of the fluid filled vessels in order to maintain neutral buoyancy. This added buoyancy is typically provided by using large quantities of materials which are less dense than water such as ceramic spheres, syntactic foam, or ultra high molecular weight polyethelene. While the added bulk from flotation is not always a drawback, such as in moored instruments, it is in the case of autonomous underwater vehicles that are mobile, where the added weight and bulk increases drag and energy expenditures, resulting in lower endurance.
In view of the above, it is an object of the present invention to provide a pressure compensating system that equalizes the pressure between the interior of a vessel and the surrounding underwater environment. Another object of the present invention is to provide a pressure compensating system that uses a compressible fluid to equalize pressure between the vessel interior and the surrounding environment. Yet another object of the present invention is to provide a pressure compensating system that uses pressure rather than volume for pressure equalization, to allow for a maximum packing efficiency of electronics, as significantly less vessel volume must be allocated for pressure equalization. Another object of the present invention is to provide a pressure equalizing system that equalizes pressure between the vessel interior and the surrounding environment as the system descends to its operating depth without requiring the use of exotic ceramic materials for the system components. Yet another object of the present invention is to provide a pressure compensating system for a vessel that uses a balance of forces to prevent implosion of the pressure vessel instead or a complicated arrangement of pressure seals. Yet another object of the present invention is to provide a pressure compensating system for a vessel that can actively reduce the pressure inside of the vessel to prevent explosion of the vessel as ambient pressure decreases. Still another object of the present invention is to provide a pressure compensating system that is easy to manufacture in a cost-efficient manner.